A methodological approach to land use-based flood

damage assessment in urban areas:

Austin case study

Alexandre Martinez

Land use of City of Austin in 2008

2010 CE394K – GIS in water resources

Taylor Johnson/American-Statesman

11/15/01: intersection of 10th and Lamar

The 1910 Great Flood in Paris

1910 – Quai de Grenelle

2

Table of Contents Executive summary ................................................................................................................................ 4

1. Introduction .................................................................................................................................... 5

1.1. Overview of flood ..................................................................................................................... 5

1.2. Historical Flooding .................................................................................................................. 6

1.3. Methodology ............................................................................................................................ 6

2. Study Area: Travis County – City of Austin ................................................................................... 7

2.1. Localization ............................................................................................................................. 7

2.2. Land Use ................................................................................................................................. 8

2.3. Population, Incomes .............................................................................................................. 10

2.4. Hydrology .............................................................................................................................. 11

2.4.1. Basins and rivers ........................................................................................................... 11

2.4.2. Watershed ...................................................................................................................... 11

2.4.3. Floodplain ...................................................................................................................... 12

3. Economics ..................................................................................................................................... 12

3.1. Purpose .................................................................................................................................. 12

3.2. Methodology .......................................................................................................................... 12

3.2.1. Natures of costs. ............................................................................................................ 12

3.2.2. Impact parameters ........................................................................................................ 13

3.2.3. Expected Annual Damage ............................................................................................. 14

3.3. Land use ................................................................................................................................ 14

3.3.1. Structural/Content Value .............................................................................................. 14

3.3.2. Flood/Damage relationships .......................................................................................... 15

4. Results .......................................................................................................................................... 17

5. Conclusion ..................................................................................................................................... 19

Glossary ................................................................................................................................................ 20

Bibliography ......................................................................................................................................... 21

Annex 1 : Austin Land use in 2008 ............................................................................................... 22

Annex 2: Watershed of Austin ...................................................................................................... 23

Annex 3: City of Austin floodplain ................................................................................................ 24

Annex 4: Population in 2000 ......................................................................................................... 25

Annex 5: Market Value of city of Austin....................................................................................... 26

Annex 6: Median Family Income in City of Austin (2008) ........................................................... 27

Annex 7: Building Permits in the City of Austin (2008) ............................................................... 28

3

Additum: Flood Management in France ........................................................................................... 29

1. French territorial organization ............................................................................................. 29

2. The SCHAPI Network ............................................................................................................... 30

1. Introduction ........................................................................................................................... 30

2. SCHAPI information ............................................................................................................. 31

4

Executive summary

My goal for this project is to conduct a flood loss study in the city of Austin. The purpose of this study

is multiple. It could be used by insurance company for insurance rate, by people who want to take the

risk to buy a house near the river or in a flood zone. It could also be companies which want to install

a factory, commercial… or just government which planed the construction of flood protection

equipments (dam…).

I decided to focus on a 2% Flood event because data are easily available. It is also flood event that can

occur and that cost a lot of money. During, this study, I had to make some choice and some

assumptions that are explained. The validity of this assumption will be discussed but this study is

the first step toward a more accurate study. My argument is that I wanted to explore the different

ways to evaluate flood losses more than to obtain a precise (or not) figure in dollars.

To finish, I will briefly introduce the French flood management system and the different actor of this

system.

5

1. Introduction

1.1. Overview of flood Floods are one of the most common hazards in the USA. Floods effects can be local, impacting a

neighborhood or community, or very large affecting entire river basins and multiple states.

However, all floods are not alike. Some floods develop slowly, sometimes over a period of days. But

flash floods can develop quickly, sometimes in just a few minutes and without any visible signs of

rain. Flash floods often have a dangerous wall of roaring water that carries rocks, mud, and other

debris and can sweep away most things in its path. Overland flooding occurs outside a defined river

or stream, such as when a levee is breached, but still can be destructive. Flooding can also occur

when a dam breaks, producing effects similar to flash floods.

Central Texas, often called “Flash Flood Alley” has been

identified as the most flash-flood prone area in the USA

by National Weather Service and holds 6 of 12 world

record rainfall rates in 24 hours or less according to the

United States Geological Survey (USGS). Some 20

million of Texas 171 million acres are flood prone (Blue

Ribbon Committee Study) and about 8 millions

structures are located in flood plains.

Be aware of flood hazards no matter where you live, but

especially if you live in a low-lying area, near water or

downstream from a dam. Even very small streams,

gullies, creeks, culverts, dry streambeds, or low-lying

ground that appears harmless in dry weather can flood.

Floods have also an economic impact and the total

economic losses can reach some astronomical

amount.

6

1.2. Historical Flooding October 17, 1998.

In Austin, 454 homes were damaged, with most of the damages incurred to houses along Onion

Creek, Walnut Creek, and Williamson Creek. Statewide, this storm caused property damages and

losses of almost $1 billion1.

May 24, 1981.

This storm event will always be remembered as the "Memorial Day Flood"2 which drowned 13 people

and caused $36 million in damages. This short duration storm with intense rainfall hit many of

Austin's urban creeks: Shoal, Walnut, Little Walnut, Bee, and Waller. Shoal Creek normally flows at

90 gallons per minute, but peaked during this flood at 6 million gallons per minute! Some areas

received over 10" of rain in four hours.

1.3. Methodology

FIGURE 1 COMPUTATION OF THE AVERAGE ANNUAL DAMAGE

The methodology used is this

report is the land use approach

because we are working

essentially on an urban area.

Crossing this information with

hazard and values data, we

should be able to define an

average annual damage on this

area as shown on figure 1.

1 http://www.ci.austin.tx.us/watershed/floodhistory.htm 2 http://www.cityofaustin.org/watershed/floods/default.htm

7

2. Study Area: Travis County – City of Austin

2.1. Localization Austin City is located in Central Texas, in an area called the

“flash flood alley” due to the strong flood events that occurred

in Texas According to the National Weather Service, flash

flooding is a rapid rise in water levels associated with heavy

rainfall or the failure of a dam or ice jam.

FIGURE 2 FLASH FLOOD ALLEY3

Because the hills to the west are primarily limestone rock with a thin covering of topsoil, portions of

the city are frequently subjected to flash floods from the runoff caused by thunderstorms. To help

control this runoff and to generate hydroelectric power, the Lower Colorado River Authority operates

a series of dams that form the Texas Highland Lakes. The lakes also provide venues for boating,

swimming, and other forms of recreation within several parks on the lake shores.4

3 http://www.floodsafety.com/media/maps/texas/index.htm

4 http://www.lcra.org/

Evaluate the losses

Combining informations for each damage

% of damage occasioned by flood event

Flood plain study Nature of damage

Evaluate value of area

Land use analysis Activity analysis

8

2.2. Land Use Land use analysis is a way to classified how land is used, each type of use having its own

characteristics. The land use plan brings together consideration for both the physical development as

well as the social characteristics of the town.

The first step of land use analysis is to conduct an inventory of different uses. The land use inventory

classified land uses into 11 major categories. The data are provided by the city of Austin.5

TABLE ‎2-1 LAND USE AND SURFACE AREA IN THE CITY OF AUSTIN IN 2008

Land use category Total Area (km²) % Area

Housing 386.9 24.13%

Single Family 259.2 16.17%

Mobile Home 28.4 1.77%

Duplex 9.8 0.61%

Large lot single family 48.1 3.00%

Apartment 38.3 2.39%

Multi family 1.3 0.08%

Group Quarters 0.4 0.03%

Retirement Housing 1.3 0.08%

Commercial 40.1 2.50%

Office 27.0 1.68%

Industrial 40.8 2.54%

Manufacturing 14.0 0.87%

Warehousing 20.1 1.26%

Equipment services 6.7 0.42%

Mining 23.2 1.45%

Civic 40.8 2.55%

Semi institutional Housing 2.0 0.12%

Hospital 0.8 0.05%

Government 7.2 0.45%

Educational 18.5 1.16%

Meeting Assembly 10.3 0.64%

Cultural services 0.2 0.01%

Cemetery 1.9 0.12%

Open space 261.8 16.33%

Parks, Open space 80.3 5.01%

Golf course 11.9 0.74%

Campgrounds 8.4 0.52%

Preserve 161.2 10.06%

Transport 166.6 10.39%

Railroad facilities 0.8 0.05%

Transportation termination 0.6 0.03%

5 Austin Land use 2008 : GIS Data set : http://www.ci.austin.tx.us/landuse/gis.htm

9

Aviation 15.9 0.99%

parking 2.1 0.13%

street 147.2 9.18%

Utilities 11.4 0.71%

Agriculture 173.2 10.81%

Undeveloped 390.7 24.37%

Water 41.0 2.55%

Total 1603.4 100%

FIGURE 3CITY OF AUSTIN LAND USE IN 2008

The open space+ agricultural and

undeveloped areas represented more than

50% of city of Austin district. Then

Housing represents 24% of areas. This is a

lot and according to the spatial land use

map, the main building near the river, so

one of the most exposed area to flood, are

houses.

Then, industrial and commercial buildings

represent only 5% of the area. It is the

building that could represent the biggest

part of losses because of the value of

inventories, and the economic activities.

The main part of buildings is housing whose repartition is shown on the chart below:

FIGURE 4 HOUSING REPARTITION OF CITY OF AUSTIN IN 2008

The inventory of property has been

conducted to determine the number and

type of structures, structure and content

values, and ground and first floor

elevations (elevation where water enters

the structure). Associated with the

inventory is the identification of an

applicable flood depth-percent damage

relationship for each structure type.

Undevelopped24%

Housing24%Open space

16%

Agriculture11%

Transport10%

Others4%

Water3%

Civic3%

Industrial3% Commercial

2%

Austin's Land use in 2008

Single Family; 67.00%

Mobile Home; 7.34%

Large lot single family; 12.44%

Appartment; 9.91%

Other; 3.32%

Housing repartition in Austin

10

2.3. Population, Incomes Travis County covers an area of 989 square miles, and had a 2000 population of 812,2806, an increase

of 41% over the 1990 population. By 2040, the population is expected to increase by 68%.

Per capita personal income was $35,094 and ranked 7th in the state.

FIGURE 5 PER CAPITA INCOME MAP

As expected, area with high flood risk is owned by people with lower income, whereas the most safe

and most expensive area is owned by people with high incomes.

6 Census- 2000

-100000

400000

900000

1400000

2000 2010 2020 2030 2040

Population

11

2.4. Hydrology

2.4.1. Basins and rivers

The city of Austin is drained by one major river, the Colorado River which is managed by the

Colorado River Authority who tries to prevent flood.

2.4.2. Watershed

There are 5 watersheds in Austin dispatched into two categories: the desired development zone and

the drinking water protected zone.

Suburban watersheds

Urban watershed

and

Desired development zone

12

Water supply suburban watersheds

Water supply rural watersheds

Barton Springs Zone

2.4.3. Floodplain

Floodplain is the most important part of this

study, they give data on which part of the city are

threatened by a flood event. For th 0.2PCT flood

event, only 11% of city of Austin area is threatened

by flood. By identification of the main area

threatened, we can say that residential area (most

especially single family housing) will be threatened

by flood whereas industrial building will be

relatively saved from the flood. Commercial

building including restaurant will be also

threatened but less than housing.

3. Economics

3.1. Purpose “Damage results from the conflict between nature made flooding and human usage. The type and

extent of damage continuously changes with development in society.” (ICPR, 2002).

3.2. Methodology The methodology used here is first to evaluate the value of an area and then to evaluate which

percentage the flood event losses represent.

The computation of flood damages is based upon the depth of flooding for various flood events

(exceedence probabilities), and a relationship between the depth of flooding and the estimated

damages based upon a percentage of the structure and content, or vehicle value.

3.2.1. Natures of costs.

An important step is to define, list and categorize the different losses that can affected an area. There

are different type of losses that involved human or animal life and a large variety of economic losses

of tangible or intangible nature. When put together, it defines the Probable Maximum Loss.

Drinking protected zone

13

Direct costs are physical damages to buildings, inventories… and can be evaluate directly by

the cost of same standard replacement.

Indirect costs are flow damages such as business interruption, cleaning costs, evacuation

costs.

Relief costs represent assistance to the affected population. It refers to services to people who

were devoid of those services because of the flood event.

A distinction should be done between tangible and intangible costs. Tangible costs can be evaluated

by an amount of dollars (such as building reconstruction or replacement, inventories….) whereas

intangible costs cannot be assessed by money (what is the price of a human life? Life insurance?

$10M?...). In this report, only tangible costs will be considered.

3.2.2. Impact parameters

There are quantities of parameters that are involved in flood impacts assessments. The most

important are:

Water height

Velocity of flood’s flow

Duration of flood

Rate of water rise during the flood

Others more specific (seasonality for agriculture…)

Flood Damage

Tangible Intangible

Indirect costs Direct costs

Financial Opportunity Clean-up Internal External Structure

Loss of

production or

revenue

Reduced

Wages

Extra

expenditure

Non

provision of

public

services

Immediate

removal of

flood debris

and

discarded

items

Content of

main

buildings

External

items: e.g.;.

Vehicles

Content of

outbuildings

sheds

Cleaning and

repair of

buildings

FIGURE 6 TYPE OF FLOOD DAMAGE

14

This is resumed in the following table:

Depending of the type of building in an affected area, a model provided allows the computation of the

losses (direct or indirect) using this information. This model is a damage function that

3.2.3. Expected Annual Damage

The Expected or Average Annual

Damage can be computed from

the land use plan and the

floodplain. Knowing the land use

type of an area, we can use the

appropriate parameters in order

to evaluate the value of this area

and so to compute the direct

costs of the flood event. The same

process could be used to evaluate

the indirect cost of the flood

event.

3.3. Land use

3.3.1. Structural/Content Value

The computation of losses by flood relies on the height/depth of flooding and relationship between the

depth and the expected damages on a vehicle or a structure, content… This damage is a percentage of

the value of the vehicle, structure or content. Using this information, we can compute the expected

damage for one year or expected annual damage (EAD).

Depth

•Housing

• Industrial

•Commercial

•Transport

•Open Space

Flow duration

•Housing

•Industrial

•Commercial

Rising rate

•Housing

•Industrial

•Commercial

Expected Annual Flood Damage

Stage damage

Stage Discharge

Flood Probability

15

For example, in this study, we would consider a 200-year frequency flood or 0.2% flood event. That

means that this flood has one percent chance to be equaled or exceeded in any given year.7

Structure values could be the current price of the structure, or the price to rebuild the structure

(replacement costs) or the price to repair the structure.

The replacement costs are not representative of the reality because it doesn’t take into account

depreciation due to deterioration occurring before the flood event and it tends to overestimate the

cost of the flood.

The reparation costs are the most useful for owners and it is that price they are looking for.

The current price could be the market price and it used by insurance companies. We can have access

to these data (market price map of city of Austin, Annex 6).

3.3.2. Flood/Damage relationships

One relationship that can be used is the depth-

percent damage relationship which relate the

depth of flooding relative to the structure (first

floor usually) and contents as a percent of the total

estimated value. First, we need to know the height

of flood, which can be computed following the next

schema. We first need to know the exceedence

probability to have the discharge of the stream and

then using USGS data, we can compute the height

of flood that we were looking for.

Discharge depth curves can me made

using USGS gauge data. For example,

using USGS 08158000 Colorado Rv at

Austin, TX 8 data, we can plot the

following discharge-depth curve for

Colorado River

7 Federal Emergency Management Agency (FEMA). 8 http://waterdata.usgs.gov/usa/nwis/uv?08158000

0

1

2

3

4

5

6

7

0 1000 2000 3000

Heig

ht

(ft)

Discharge (ft3/sec)

Discharge depth curve

for Colorado River, TX

16

For this analysis, generalized curves for residential structures were developed by the Colorado River

Authority. The relationships used in this study are based upon generalized curves compiled by the

U.S. Federal Emergency Management Agency, Flood Insurance administration. The next table

displays the depth-percent damage relationship for the most prevalent structure type (single

residential). The other values can be estimated using a linear regression relationship.

This model applies only for residential house and also for industrial/commercial or civic building, but

not for open space and transportation areas. Also remained that the losses by cessation of economic

activities of industrial or commercial building are not taken into account in this study.

Stage Structure Contents Stage Structure Contents

m % % m % %

-2 0 0 9 70.5 37.2

-1 2.5 2.4 10 73.2 38.4

0 13.4 8.1 11 75.4 39.2

1 23.3 13.3 12 77.2 39.7

2 32.1 17.9 13 78.5 40

3 40.1 22 14 79.5 40

4 47.1 25.7 15 80.2 40

5 53.2 28.8 16 80.7 40

6 58.6 31.5 20 85 50

7 63.2 33.8 30 85 60

8 67.2 35.7 40 85 70

0

20

40

60

80

100

-10 0 10 20 30 40

Percen

t D

am

ag

e

Stage (inches)

Depth-Percent Damage

Function

Structure %

Contents %

inche

s

inche

s

17

4. Results I use a 0.2 percent annual chance exceedance (data available on city of Austin website).

The first step is to integrate the floodplain on ArcMap software and also the land use map and value

map. Then we can compute damages using a raster calculator using the flood-damage relationships

developed below.

For instance, on Thurgood Avenue, we obtain the following results:

This can be summarizing on:

For this area, there is one single family house which

is affected by a 0.2 % Flood. The depth is 1 foot so

the % of losses if 77% for building and 31% for

content. The land market value is $450,000 so the

expected annual damages for this area are $350,000.

If we collect all the data of all the area of Austin, we obtain the following table in $1000.

Number Structure Content Total

Single Family 932 313 844.00$ 156 923.00$ 470 767.00$

Multifamily 45 11 058.00$ 5 529.00$ 16 587.00$

Commercial 85 32 552.00$ 25 471.00$ 58 023.00$

Public 40 21 154.00$ 8 583.00$ 29 737.00$

Residential 403 5 445.00$ 6 206.00$ 11 651.00$

Land Use Layer 100 = Single Family

Market Value Layer 450 765.00$

0.2 PCT ACE

1 foot

Building% 77

Content % 32

Losses 347 089.05$

Flood Plain Layer

Thurgood Avenue

18

$-

$100 000.00

$200 000.00

$300 000.00

$400 000.00

$500 000.00

Str

uctu

ra

l D

am

ag

es (

$1000)

Expected Annual Damage

19

5. Conclusion

To conclude, the cost analysis of a flood can be leaded of several ways. Depending of the goal of the

study, the parameters taken into account or the losses considerate will not been the same. An

insurance company will focus more on the buildings and contents whereas a governmental

organization will focus more on the economic activities and lead a cost-benefit analysis.

I have tried to evaluate some losses (only properties) in the city of Austin. The main difficulty

encountered was to collect significant data for a specific area. Lots of data are available but

sometimes, data are missing or are not accurate enough.

I decided to lead a land used analysis first to estimate which parts of the cities were threatened. It

appears that housing were the main threatened buildings. This could represent so lot of losses for

insurance company, and require strong human and technical resources for civil protection.

Prevention of flood or forecasting of flood is so important for the Travis County. A cost-benefice

analysis of protection equipments could use these results to evaluate the efficiency of such

constructions.

20

Glossary

1% Annual

Chance Flood

To provide a national standard without regional discrimination, the 1% annual

chance (100-year) flood has been adopted by the Federal Emergency

Management Agency (FEMA) as the base flood for floodplain management and

flood insurance purposes. A 1% annual chance flood (or base flood) has a 1%

annual chance of being equaled or exceeded in any given year.

1% Annual

Chance

Floodplain

The 1% annual chance floodplain identifies areas that are expected to be

inundated by the 1% annual chance flood. The 1% annual chance floodplain,

shown on a Flood Insurance Rate Map, is also called a Special Flood Hazard

Area, where the National Flood Insurance Program’s floodplain management

regulations must be enforced by the community as a condition of participation

in the Program.

Base Flood

Elevation

(BFE)

BFEs are shown on a Flood Insurance Rate Map and represent rounded,

whole-foot elevations of the 1% annual chance flood at selected locations along

flooding sources that have been studied in detail. To reduce the risk of damage

from floods up to the 1% annual chance flood, communities are advised to

consider these elevations when issuing building permits for structures.

Digital Elevation Model (DEM)

A DEM is a file with terrain elevations recorded for the intersection of a fine-

grained grid and organized by quadrangle as the digital equivalent of the

elevation data on a topographic base map.

Flood Insurance Rate

Map (FIRM)

The FIRM illustrates the extent of flood hazards in a community by depicting

a variety of types of information. This information may include flood insurance

risk zones, 1% and 0.2% annual chance floodplains, floodways, base flood

elevations or depths, common physical features such as roads and streams,

and the location of cross sections. New FIRM panels for North Carolina have

been produced digitally, and the data shown on these panels are available in

the public domain.

Flood Insurance Study (FIS)

The FIS is an examination, evaluation, and determination of flood hazards,

and, if appropriate, corresponding water-surface elevations. The FIS includes

the FIS Report, Flood Insurance Rate Map panels, flood profiles, and tables.

Floodplain Management

The operation of an overall program of corrective and preventive measures for

reducing flood damage, including, but not limited to, emergency preparedness

plans, flood control works, and floodplain management regulations.

National Flood Insurance Program

(NFIP)

Administered by FEMA, the NFIP enables property owners in participating

communities to purchase insurance protection against losses from flooding,

provides a framework for a community’s floodplain management ordinances,

and identifies floodplain areas and flood risk zones.

Watershed The area draining into a river, river system, or body of water.

21

Bibliography

A., B. (2004). Vurrent and future impacts of flooding in urban areas, Case study: Pordenone

province, Italy.

Betts. (2002). Flood damage analysis using GIS at Gold Coast City Council. Australian

Journal Emergency Management .

David, M. (2000). Creating an ArcGIS Hydro Data Model Extension for Flood Plain

Mapping.

Erdlenbrucht, K., Gilbert, E., Grelot, F., & Lescoulier, C. (2008). Une analyse Cout Benefice

spatialisée de la protection contre les innondations - Application à la vallée de l'Orb.

FEMA. (2010). Benefit Cost analysis.

Government, Q. (2002). Guidance on the Assessment of Tangible flood damages.

Merz, A., Kreibich, H., Schwarze, R., & A., T. (2010). Assessment of economic flood damage.

Natural Hazards and Earth System Sciences , 1697-1701.

Merz, B., Kreibich, H., Schwarze, R., & Thieken, A. (2010). Assessment of economic flood

damage. Natural Hazards and Earth System Sciences .

Messner, F., & al. (2006). Guidelines for Socio-economic Flood Damage Evaluation.

22

Annex 1 : Austin Land use in 2008

Land use of the city of Austin: layout from ArcMap10

23

Annex 2: Watershed of Austin

Watersheds regulation areas of the city of Austin: layout from ArcMap 10

24

Annex 3: City of Austin floodplain

City of Austin Floodplain, layout from ArcMap 10sd

25

Annex 4: Population in 2000

Population repartition in the city of Austin in 2000 – Layout from ArcMap 10

26

Annex 5: Market Value of city of Austin

Land Value (market value) in 2000 – data from Census Bureau – Layout from ArcMap 10

27

Annex 6: Median Family Income in City of Austin (2008)

28

Annex 7: Building Permits in the City of Austin (2008)

Building Permis in 2008 – data from City of Austin – Layout from ArcMap 10

29

Additum: Flood Management in France

1. French territorial organization

France is divided in 26 “régions” and subdivided in 100

“départements”. There are about 36600 “communes”. Mayors these

communes are responsible for public safety and are supported by the

State which provides flood information and implements a flood alert

system.

The territory organization for weather or flood-rain forecasting,

used by Météo France is the same as the administrative one,

there are 22 regions and so 22 regional centers. Moreover,

there are several UH (Unité d’Hydrométrie: hydrometric units)

all along the territory which provides data to the centers.

The territory organization for flood surveillance, used by

SCHAPI in France is quite differently from the administrative

one. There are also 22 SPC (“Service de prevision des crues”:

Service of flood forecasting). These areas follow the main rivers

and watershed of France.

9

France is not spared by flood events as evidenced the 1910

great flood in Paris which is considered as a 100-year flood.

9 Source : Geoportail : http://www.geoportail.fr/?l=EMPRISE-CRUE(55),Photo

30

2. The SCHAPI Network

1. Introduction

SCHAPI stands for Service central d’hydrométéorologie et d’appui à la prévision des inondations or

Central Service of Hydrometeorology and Support for Flood Forecasting.

SCHAPI is located in the heart of Toulouse in order to promote synergy between Météo-France and

the scientific teams which are in Toulouse. The SCHAPI provides flood forecasting 24/24, 7/7.

Meteorologist, hydrologist and computer scientists are working in direct contact and with a network

of partners.

The SCHAPI is at the heart of an operational network of flood and rainfall forecasting. This network

gather 22 SPC and 28 UH but is also in interaction with many scientific and technical partners as

shown in the following map:

The SCHAPI holds an important role in flood forecasting. The first motivation for its creation in June

2003 was to better understand the threat of “Cévenol” thunderstorms10 and flash flood. Its field of

10 A Cévenol thunderstorms is a storm that occurs in the Cevennes (south of France)

31

intervention was quickly extended to all flood risk and included the modernization and management

of the national database of hydrometric data.

This operational network is working according to the following map:

The SPC 11 provide forecasting for major watersheds.

Forecasters of the 22 SPC analyze the rivers and the watershed

fed. They deduce a level of alertness (level of risk) by

segment/section streams, resulting in a color code (green for no

particular risk, yellow is fast rising, orange is risk of significant

damage, red is risk if serious damage).

2. SCHAPI information

SCHAPI website (vigicrues.fr) provides all the information collected in a map updated twice a day (10

am and 4 pm) or more if necessary. There are 3 levels of details.

The first level is a national map. There is a color scheme used

(green for no risk, 1 for small risk, 2 for moderate risk, 3 for

high risk). That is color scheme used by Météo France that is

well known and so easy to understand for French people.

The second level of detail is a regional map. The

region concerned is one of the 22 SPC. The

same color scheme is used. There is also the

possibility to see details for sections. SCHAPI

watch about 20,000 km of sections of rivers in

Metropolitan France.

11 Remind : Service of flood forecasting.

SCHAPI

UH SPC

32

The third and last level of detail is the water

level (height) or flow of a station (UH) which is

on a section of a river. There is possibility to

display the rate of flow or height of other

stations of the same section. The dotted curve

is the data of the last significant flood.